Position measuring device

ABSTRACT

A position measuring system that includes a scale graduation, a scanning unit for scanning the scale graduation. An adjustment device that includes a displacement element for setting a position of the scanning unit with respect to the scale graduation and a gear-down mechanism arranged between the displacement element and the scanning unit, the gear-down mechanism converts a displacement movement of the displacement element into a shorter displacement movement of the scanning unit. The gear-down mechanism includes a lever arrangement with joints, which converts the displacement movement of the displacement element into a linear displacement movement of the scanning unit in relation to the scale graduation.

[0001] The invention relates to a position measuring system inaccordance with the preamble of claim 1.

[0002] Such a position measuring system is known from DE 43 17 022 C1.The position of a scanning unit with respect to a graduated disk isadjusted by means of a displacement element of an adjustment device inthat the displacement element in the form of a screw acts on a lever ofa reduction mechanism and displaces the scanning unit in a geared-downmanner. This displacement movement is a pivot movement around a flexiblejoint of the adjustment device.

[0003] In accordance with DE 28 44 066 A1 and DE 40 01 848 C1, thedisplacement also takes place by means of a lever which pivots thescanning unit around a flexible joint.

[0004] However, linear displacement movements of the scanning unit withrespect to the scale graduation are demanded in actual use, such as hasbeen explained in EP 0 158 066 A1, for example. For adjusting fourphotoelectric barriers, which are arranged spatially offset with respectto each other, of a scanning unit of an angle measuring system, thescanning unit can be displaced in the radial direction via elongatedholes. There, the radial displacement is called parallel displacementand takes place by means of two elongated holes. However, a fineadjustment is not possible with this.

[0005] It is therefore the object of the invention to disclose aposition measuring system with an adjustment device, by means of whichthe scanning device can be linearly displaced with respect to the scalegraduation in a highly accurate manner.

[0006] In accordance with the invention, this object is attained by aposition measuring system with the characteristics of claim 1.

[0007] The advantage obtained by means of the invention lies in that thescanning unit can be linearly displaced in a highly accurate manner bymeans of a simple device. The displacement movement of a displacementelement is converted in a geared-down manner into a linear displacementmovement, by means of which a delicate setting is made possible.Moreover, it is possible to provide a reduced structural size.

[0008] Advantageous embodiments are recited in the dependent claims.

[0009] The invention will be explained in still greater detail in whatfollows by means of exemplary embodiments. Shown are in:

[0010]FIG. 1, a view from above on an angle measuring system with anadjustment device,

[0011]FIG. 2, the adjustment device in accordance with FIG. 1 in anenlarged representation,

[0012]FIG. 3, the adjustment device in a further adjusting position,

[0013]FIG. 4, a second embodiment of the adjustment device,

[0014]FIG. 5, a third exemplary embodiment of the adjustment device,

[0015]FIG. 6, a fourth exemplary embodiment of the adjustment device,

[0016]FIG. 7, a fifth exemplary embodiment of the adjustment device.

[0017] The angle measuring system in accordance with FIG. 1 consists ofa graduated disk 1, which is rotatably seated around the axis ofrotation D. The graduated disk has an incremental angle graduation 2 asa scale graduation, whose graduation marks are radially oriented. Ascanning unit 4 is adjustably fastened on a stator 3 for measuring therotated position of the graduated disk 1 with respect to the stator 3.The scanning unit 4 is designed in a known manner, so that only thescanning grating 5 of the scanning unit 4 is represented in FIG. 1.

[0018] The scanning unit 4 is attached to a support 16 of an adjustmentdevice 10. The adjustment device 10 has two levers 11 and 12 with stopfaces 11.10 and 12.10. These stop faces 11.10 and 12.10 are used in aknown manner (DE 32 28 507 C2) for aligning the scanning unit 4 withrespect to the graduated disk 1. For this purpose a centering collar 6,which extends concentrically with respect to the axis of rotation D andon which the adjustment device 10 is brought into contact with the stopfaces 11.10 and 12.10, is provided on the stator 3 in which thegraduated disk 1 is seated. The diameter of the centering collar 6 issubject to tolerances, so that the radial seating of the scanning unit 4by means of the centering collar 6 does not always meet the demands. Forcompensating diameter tolerances of the centering collar 6, the scanningunit 4 must be displaced exclusively radially, without changing thealignment with respect to the axis of rotation D (direction R) linearly.This linear displacement is performed with the adjustment device 10 andwill be further explained by means of FIG. 2.

[0019] As shown on a magnified scale in FIG. 2, the adjustment device 10consists of a symmetrically constructed lever mechanism, having twolevers 11, 12, each of which can be pivoted around a flexible joint 14,15 by means of a common displacement element 13. The flexible joints 14,15 are arranged between the support 16 of the scanning unit 4 and thelevers 11, 12, and are embodied in the form of weakest point joints, sothat the adjustment device 10 can be manufactured in one piece.

[0020] Each one of the two levers 11, 12 has a short lever arm 11.1,12.1 and a longer lever arm 11.2, 12.2, extending from the flexiblejoint 14, 15. The common displacement element 13, with which the twolonger lever arms 11.2, 12.2 are pivoted in opposite directions aroundthe flexible joints 14, 15, acts on the two longer lever arms 11.2,12.2. The stop faces 11.10, 12.10 are formed on the shorter lever arms11.1, 12.1. The movement of the displacement element 13 is converted bythe two lever arms 11, 12 in a geared-down manner into an oppositelydirected movement of the two stop faces 11.10, 12.10. Since the two stopfaces 11.10, 12.10 are kept in contact with the centering collar 6, thesupport 16, and therefore the scanning unit 4, moves linearly in theradial direction R when the displacement element 13 is actuated.

[0021] It is particularly advantageous if the two lever arms 11.2, 12.2are connected with each other via a common yoke 17, on which thedisplacement element 13 acts. The yoke 17 connects the two long leverarms 11.2, 12.2 in one piece with each other and is designed as aflexible beam, or deformation member. The displacement element in theform of a screw 13 acts against the center of the yoke 17 and bends theyoke 17 in the radial direction R. In the process the screw 13 issupported on the support 16. The deformation of the yoke 17 causes ashortening of the yoke 17, and thus the pivoting of the two levers 11and 12 over respectively identical distances in opposite directions. Tointroduce the pivot movement into the levers 11, 12, it is advantageousif a flexible joint 18, 19 is respectively arranged between the yoke 17and the longer lever arms 11.2 and 12.2.

[0022] Once the radial position of the scanning unit 4 has beencorrectly set by the adjustment device 10 with the gear-down mechanismconsisting of the levers 11, 12 and the flexible joints 14, 15, it isfixed in place on the stator 3 by fastening means, not represented. Thefastening bores 7, 8 provided for this are schematically represented inFIG. 2.

[0023] A displacement of the scanning unit 4 transversely to the radialdirection R is also possible by means of the adjustment device 10. Afurther displacement element 9 is provided for this purpose, which actson one of the two longer lever arms 11.2, 12.2 and deflects ittransversely with respect to the radial direction R. This exemplaryembodiment is represented in FIG. 3.

[0024] In FIGS. 2 and 3 the levers 11, 12 are shown by solid lines inthe non-deflected position, and by dashed lines in the deflectedposition, i.e. the adjusted position.

[0025] Alternatively to the yoke 17 in the form of a deformation member,the coupling of the two levers 11, 12 can be performed by means of adisplacement element 130 in accordance with FIG. 4. For the pivoting ofthe two levers 11, 12, they are connected with each other by means ofthe screw 130. When turning the screw 130, the two levers 11, 12 move inopposite directions over identical distances.

[0026] If only one of the levers 11, 12 is to be pivoted, the screw 130must be supported on a portion of the stator 3 (stator 3 represented inFIG. 3), or on the support 16, which is indicated by the locking ring30.

[0027] In a manner not represented, instead of a screw, the displacementelement 13 in accordance with FIG. 3 can also be an eccentric, whoseeccentric surface is in contact with the yoke 17 for bending the latteror, for deflecting only one lever 11, 12, it can be in contact with thelatter. In the exemplary embodiment in accordance with FIG. 4, theoppositely directed displacement of the two levers 11, 12 can also beprovied by a wedge which acts simultaneously on the two levers 11, 12.

[0028] In connection with the exemplary embodiments so far explained, inthe course of adjustment it is necessary to advance the entireadjustment device 10 with the scanning unit 4 on the centering collar 6.In the exemplary embodiment explained in what follows, the adjustmentdevice 10 can be rigidly fixed in place on the stator 3 by means of astationary element 20, and the scanning unit 4 can be set in relation tothis stationary fixed element 20 of the adjustment device 10. For thispurpose, the adjustment device 10 is aligned on the centering collar 6by means of the stop faces 11.10, 12.10 and is fixed in place. Thefastening bores 27 and 28 are provided for fixing the stator 3 in place.

[0029] The support 16 of the scanning unit 4 can be displaced via agear-down mechanism in the radial direction R with respect to thestationary element 20, analogous to the already explained exemplaryembodiments. Parts with the same function are provided with the samereference numerals in all exemplary embodiments.

[0030] The gear-down mechanism again consists of a laterally-reversedlever arrangement with two levers 11, 12, which can be pivoted inopposite directions by means of a displacement element 13. The levers11, 12 are hinged on the stationary element 20 via flexible joints 14,15, and are connected with each other by means of a common yoke 17. Theyoke 17 again is a deformation member, on whose center the displacement13 acts. With a centered bending of the deformation member, the commonconnection between the two levers 11, 12 is shortened, which results ina deflection of the two levers 11, 12 over identical distances inopposite directions. In this case the displacement element 13 can besupported on the stator 3 or, in accordance with FIG. 6, on the support16.

[0031] The pivot movement of the two levers 11, 12 is transmitted in ageared-down manner to the support 16 with the scanning unit 4. The pivotmovement performed by the long lever arm 11.2, 12.1 is passed on to theshorter lever arm 11.1, 12.1. The further transfer takes place by meansof respective guide rods 21, 22 in the form of a pushrod, one end ofwhich is fastened on the short lever arm 11.1, 12.1, and the other endon the support 16. The one end of each guide rod 21, 22 is fastened viaa flexible joint 23, 24 on the short lever arm 11.1, 12.1, and the otherend via a further flexible joint 25, 26 on the support 16. The guiderods 21, 22 convert the pivot movement of the two levers 11, 12 into alinear displacement movement of the support 16 exclusively in the radialdirection R. In this way the scanning unit 4 is coupled via the twofastening points in the form of flexible joints 25, 26 with the leverarrangement 11, 12 and the guide rods 21, 22. By means of the guide rods21, 22 the pivot movement of the levers 11, 12 is converted into aparallel displacement of the two fastening points.

[0032] The adjustment devices in accordance with FIGS. 5 and 6additionally permit an adjustment of the scanning unit in a directiontransversely to the radial direction R in that—as represented in FIG.3—a further displacement element 9 only acts on one of the two levers11, 12.

[0033] After an adjustment has been performed, the scanning unit 4 isfixed in place on the stator 3. Fastening bores 7, 8 are provided forthis purpose on the support 16.

[0034] Analogously with the exemplary embodiment of FIG. 4, the twolevers 11, 12 can also be connected with each other by means of a commonscrew 130, as represented in FIG. 7.

[0035] It is particularly advantageous if all levers 11, 12 and flexiblejoints 14, 15, 18, 23 to 26 of the gear-down mechanism are located on acommon plane and are manufactured in one piece. The axes of rotation ofthe flexible joints 14, 15, 18, 23 to 26 are aligned parallel with eachother.

[0036] The device in accordance with the invention can also be employedfor adjusting the scanning unit in other straight-line movementdirections, for example for setting the scanning distance between thegraduation 2 and the scanning grating 5. Moreover, the invention is notlimited to the described angle measuring system. In place of a graduateddisk 1, the scale graduation can be merely a sector, or a linear scale.The scale graduation can be designed to be scanned photoelectrically,capacitively, magnetically or inductively. The graduation can be anincremental periodic graduation or an absolute single-track ormulti-track coding.

1. A position measuring system, comprising a scale graduation (2), ascanning unit (4) for scanning the scale graduation (2), an adjustmentdevice (10) with a displacement element (13, 130) for setting theposition of the scanning unit (4) with respect to the scale graduation(2), wherein a gear-down mechanism is arranged between the displacementelement (13, 130) and the scanning unit (4), which converts adisplacement movement of the displacement element (13, 130) into ashorter displacement movement of the scanning unit (4), characterized inthat the gear-down mechanism has a lever arrangement (11, 12) withjoints (14, 15, 18, 19, 21, 22, 23, 24), which converts the displacementmovement of the displacement element (13, 130) into a lineardisplacement movement of the scanning unit (4) in relation to the scalegraduation (2).
 2. The position measuring system in accordance withclaim 1, characterized in that the displacement element (13, 130) actssimultaneously on two levers (11, 12), and each of the two levers (11,12) is seated so that it is pivotable around a flexible joint (14, 15).3. The position measuring system in accordance with claim 2,characterized in that the two levers (11, 12) are coupled together bymeans of a yoke (17), on which the common displacement element (13)acts, wherein the two levers (11, 12) can be pivoted in oppositedirections when the displacement element (13, 130) is actuated.
 4. Theposition measuring system in accordance with claim 3, characterized inthat the yoke (17) is a deformation member, which is formed in one pieceon the two levers (11, 12).
 5. The position measuring system inaccordance with one of the preceding claims, characterized in that theadjustment device (10) has stop faces (11.10, 12.10) spaced apart fromeach other, by means of which the scanning unit (4) can be oriented withrespect to the scale graduation (2), and that these stop faces (11.10,12.10) can be displaced over the lever arrangement (11, 12) by means ofa common displacement element (13, 130).
 6. The position measuringsystem in accordance with claim 5, characterized in that the scalegraduation (2) is an angle graduation (2), which is seated in a stator(3) and can be rotated around an axis of rotation (D), and a centeringcollar (6), which extends concentrically with respect to the axis ofrotation (D), is arranged on the stator (3), against which theadjustment device (10) rests by means of two stop faces (11.10, 12.10),and the lever arrangement (11, 12) for displacing the stop faces (11.10,12.10) is arranged between the displacement element (13, 130) and thestop faces (11.10, 12.10).
 7. The position measuring system inaccordance with claim 6, characterized in that the lever arrangementcomprises two levers (11, 12), each of which can be pivoted in oppositedirections around a respective flexible joint (14, 15), wherein one ofthe flexible joints (14, 15) is respectively arranged between thescanning unit (4) and one of the levers (11, 12).
 8. The positionmeasuring system in accordance with claim 7, characterized in that eachone of the two levers (11, 12) has a short lever arm (11.1, 12.1)extending from the flexible joint (14, 15), and a longer lever arm(11.2, 12.2) extending from the flexible joint (14, 15), wherein thedisplacement element (13, 130) acts on the longer lever arm (11.2,12.2), and one of the stop faces (11.10, 12.10) is arranged on theshorter lever arm (11.1, 12.1).
 9. The position measuring system inaccordance with one of claims 1 to 4, characterized in that theadjustment device (10) has a stationary element (10), to which thescanning device (4) is coupled by means of flexible joints (25, 26), andthe flexible joints (25, 26) can be displaced parallel to each other onthe scanning unit (4) by means of the lever arrangement (11, 12). 10.The position measuring system in accordance with claim 9, characterizedin that the lever arrangement consists of two levers (11, 12), wherewithrespectively one lever (11, 12) acts on one of the flexible joints (25,26) of the scanning unit (4), and the two levers (11, 12) can be pivotedtogether via the displacement element (13, 130).
 11. The positionmeasuring system in accordance with claim 10, characterized in that thetwo levers (11, 12) are coupled to a guide rod (21, 22), which convertsthe pivot movement of the levers (11, 12) into a parallel movement ofthe flexible joints (25, 26) of the scanning unit (4).
 12. The positionmeasuring system in accordance with claim 11, characterized in that eachof the guide rods (21, 22) is coupled to the scanning unit (4) by meansof the respective flexible joint (25, 26), and they are coupled to thelever (11, 12) by means of a further flexible joint (23, 24).